Steam Explosion Modification of Soybean Dregs to Enhance High-solid Enzymatic Hydrolysis Efficacy

Objective: The modification of bean dregs by steam explosion (SE) combined with high solids enzymatic digestion to extract soluble dietary fiber (SDF) was investigated to evaluate the modification effect of soybean dregs and the enhancement of the high solid enzymatic digestion process. Methods: The bean dregs were modified by SE technology. The microstructure, chemical composition, functional groups and thermal stability of bean dregs before and after SE modification were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and differential scanning calorimetry. SDF was prepared by SE combined with high-solid enzymatic hydrolysis, and the enzymatic hydrolysis effect of bean dregs before and after SE was compared. Results: The SE treatment significantly improved the structure and properties of soybean dregs, which contributed to the conversion of insoluble dietary fiber (IDF) into SDF. The SDF content of soybean dregs was increased to 3.85 times that of raw materials under the optimal SE condition. After SE, the microstructure of bean dregs showed a loose honeycomb porous structure, the water solubility was increased by 5.13 times, and the water holding capacity, oil holding capacity and water swelling were reduced. The maximum pyrolysis peak temperature and enthalpy change of soybean dregs were increased and the thermal stability was improved. The composition and structure of enzymatic substrates and the flow state of enzymatic system were prompted by SE, so as to reduce the solid load restriction of enzymatic hydrolysis process of soybean dregs. It benefited to increase the concentration of the enzymatic substrate, lower the amount of enzymes and the enzymatic hydrolysis time. Under the enzymatic hydrolysis conditions at the maximum solid loading of 20% and the minimum enzyme consumption of 5 FPU/g, the yield of SDF in SE bean dregs reached 43.75%, which was 3.76 times higher than that of raw materials. Through SE, the reaction equilibrium time of enzymatic hydrolysis was decreased by about 50%. Conclusion: SE modification combined with high-solid enzymatic hydrolysis treatment technology would provide technical support for the efficient utilization and application for the large amount of bean dregs.